As chief materials in pharmaceutical/medical rubber compounds represented by pharmaceutical/medical containers and sealable articles, plasticizedpolyvinyl chloride resin, and natural rubber, butyl rubber, isoprene rubber, styrene-butadiene rubber and the like have been used conventionally.
Plasticized polyvinyl chloride resin is excellent in softness and flexibility, but on the other hand, is accompanied by such problems that a plasticizer may bleed out and that ethylene oxide may remain upon sterilization with ethylene oxide. On the other hand, the use of the latter rubber materials involves such problems that large equipment is needed as they generally require a vulcanization step and that a crosslinking agent may dissolve out. To lessen the se problems, Patent Document 1, for example, proposes pharmaceutical/medical articles made of a block copolymer of an aromatic vinyl compound and isobutylene, and further, Patent Document 2 proposes pharmaceutical/medical containers made of a similar block copolymer as described above.    Patent Document 1: JP-A-5-212104    Patent Document 2: JP-A-5-269201
These block copolymers permit injection molding and require no crosslinking step, so that they are superior in moldability and economy to conventional rubber materials. Moreover, no crosslinking agent or the like is used, and therefore, the problem of its dissolution into medicaments has been resolved. Molded rubber articles according to the technologies proposed in the above-described Patent Documents 1 and 2 are, however, still accompanied by a serious problem in that they undergo significant permanent set under stress especially at high temperatures (during drying, sterilization treatment or the like). In addition, they are insufficient in rubber elasticity and are brittle even at room temperature, and are not sufficient either in inertness with medicaments.